Audio Passthrough on LiveTV

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Bluebrain Offline
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Post: #16
I just found out how Dolby Digital in Live TV still (or again?) works:

set your audio configuration to 2.0 channels, activate passthrough and(!) "enable Dolby Digital (AC3) transcoding"

Now both, video files and Live TV 5.1 is working fine with my Fire TV (v1).
I checked with an ac3 test file and Live TV (Star Wars, e.g. the spaceships were clearly hearable coming from the back, flying to the front)
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skybird1980 Offline
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Post: #17
You get DD 2.0 then.. Great.
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Bluebrain Offline
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Post: #18
No, definitely not. I get 5.1!
As I wrote, I double checked it, if there are really 6 separate channels transmitted.
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nexusle Offline
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Post: #19
Bluebrain is right. I also get 5.1 but audio and video are asynchronous then...
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ampeer Offline
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Post: #20
May I ask what exactly a "live stream" is in this case? If I press pause on live TV and resume after 5 minutes, is this still "live"? And what about watching a recorded TV show? There is still no passthrough when played from Kodis PVR listing (although this is not live at all).

But with network share access to the recording folder I can play the same recording from Kodis Video section using passthrough without any issues. Where exactly is the difference? Maybe @FernetMenta can clarify?

(Don't get me wrong I very very much appreciate the work you guys are doing on Kodi. This is simply great! I just hope that my feedback might help to improve Kodi)

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FernetMenta Offline
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Post: #21
"live stream" is the wrong expression in this context. It is called realtime, that means data comes in in the speed of playback. Video player asks the inputstream (in case of PVR, the PVR backend) if the stream is realtime.
If you get no passthrough on a recording, this is most likely an issue with the pvr addon you have in use.
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CiNcH Offline
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Post: #22
DVBViewer Client add-on currently always returns True, also when timeshifting. So it is always a realtime stream, hence no passthrough.

Sony BRAVIA 2015 (FW V3.865 / Android TV 6.0.1) | DVBViewer Media Server 2.0
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mattlach Offline
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Post: #23
Well, I just upgraded from Jarvis to Krypton.

In Jarvis audio passthrough in LiveTV with the MythTV plugin worked perfectly. Passed through streams correctly identified by the receiver, and no syncing issues what so ever.

I just updated to Krypton. Passthrough still works in LiveTV, I don't find it blocked like some report above, but the syncing is HORRIBLE. It starts in sync, but over time gets so far out of sync that even the receivers auto lipsync feature cant compensate for it.

If live tv audio passthrough can not be done due to sync issues, how come it worked perfectly in Jarvis?

I may have to figure out how to downgrade back to Jarvis, because the current state is completely unacceptable.

Sample:



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mattlach Offline
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Post: #24
(2017-01-01 18:50)Bluebrain Wrote:  I just found out how Dolby Digital in Live TV still (or again?) works:

set your audio configuration to 2.0 channels, activate passthrough and(!) "enable Dolby Digital (AC3) transcoding"

Now both, video files and Live TV 5.1 is working fine with my Fire TV (v1).
I checked with an ac3 test file and Live TV (Star Wars, e.g. the spaceships were clearly hearable coming from the back, flying to the front)


AC3 transcoding was enabled in my sample video above. Sad

I wonder if the fact that the final release of Krypton prevents prevents passthrough when "Player -> Sync Playback to Display" is enabled has anything to do with it.

The reason for this is stated as Sync Playback to Display would require transcoding of audio, and we can't transcode passed through audio. But if we can transcode AC3 why do this?
(This post was last modified: 2017-02-12 22:44 by mattlach.)
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mattlach Offline
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Post: #25
(2017-02-12 22:35)mattlach Wrote:  
(2017-01-01 18:50)Bluebrain Wrote:  I just found out how Dolby Digital in Live TV still (or again?) works:

set your audio configuration to 2.0 channels, activate passthrough and(!) "enable Dolby Digital (AC3) transcoding"

Now both, video files and Live TV 5.1 is working fine with my Fire TV (v1).
I checked with an ac3 test file and Live TV (Star Wars, e.g. the spaceships were clearly hearable coming from the back, flying to the front)


AC3 transcoding was enabled in my sample video above. Sad

I wonder if the fact that the final release of Krypton prevents prevents passthrough when "Player -> Sync Playback to Display" is enabled has anything to do with it.

The reason for this is stated as Sync Playback to Display would require transcoding of audio, and we can't transcode passed through audio. But if we can transcode AC3 why do this?

So, here is what I suspect happened, but with more detail:

After I upgraded to Krypton, passthrough stopped working all together. It required me to disable "Player -> Sync Playback to Display" for passthrough to work. In Jarvis this wasn't a requirement. The reason why is listed in the config description:

(Yes, this is Krypton, I just switched the skin back to Confluence, as I didn't want to have to teach everyone in the house how to use the TV again, they already complain it is too complicated)

[Image: 32484947730_3e7c3bfbbd_z.jpg]

So the reason is that if this is enabled, resampling might be required, and the assumption is that kodi can't resample passed through audio.

But then under System -> Audio -> Audio Passthrough there's this:

[Image: 32712634212_a87abd1da4_z.jpg]

It would seem as if AC3 transcoding would solve this sync problem. Is the fact that "Player -> Sync Playback to Display" is forced to be off in order to enable passthrough preventing the AC3 passthrough in the passthrough menu from working?

It seems like a mistake to disable passthrough if "sync playback to display" is enabled for this reason. Any thoughts?

The question is, how can I work around this for now?

What if, instead of using passthrough, I do all audio decoding in Kodi and present my receiver with multichannel PCM in 5.1?

If I have a 7.1 receiver (running with 5.1 speakers, two speakers are unpopulated for future upgrades) do I lose anything by going with this approach? I know it will probably increase CPU load on my Kodi box as it now has to do all the decoding, but it is a Haswell i5-4570T, so I think it can handle it no problem.

So, TLDR version, do I lose anything at all by moving to multichannel PCM with decode happening in Kodi instead of on my receiver? Will this fix my sync issue by allowing me to enable "sync playback to display"?
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nickr Offline
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Post: #26
Yes PCM will give you multichannel. I am not sure what effect sync playback to display will have.

If I have helped you or increased your knowledge, click the 'thank user' button to give thanks :) (People with less than 20 posts won't see the "Thank you" button.)
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mattlach Offline
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Post: #27
(2017-02-12 23:38)nickr Wrote:  Yes PCM will give you multichannel. I am not sure what effect sync playback to display will have.

I appreciate your response.

I guess what I am trying to figure out is, if I tell Kodi to decode the audio and present it to my receiver as 5.1 channel multichannel PCM, will this sound any different (worse?) than passing through the encoded stream to my receiver? Does the receiver do some other sort of processing magic to the stream when decoding it that Kodi doesn't?

Essentially, by using this as a workaround to get synced audio in LiveTV streams, am I giving anything up?

Also, is it better to have Kodi send the receiver 5.1 multichannel PCM to match my speakers, or is it better to have Kodi send 7.1 multichannel PCM to my 7.1 receiver, and let my receiver use Neural X or some other tech to mix it down to my 5.1 speakers?

(Bear with me here, as I am pretty new to surround stuff)
(This post was last modified: 2017-02-12 23:56 by mattlach.)
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nickr Offline
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Post: #28
There should be no difference in sound quality, although if the audio coming from your TV broadcaster is EAC3 (ie extended not plain ac3) then another thread tells me there might be problems.

Set speakers on 5.1 (in kodi) if you have 5.1 real speakers.

If I have helped you or increased your knowledge, click the 'thank user' button to give thanks :) (People with less than 20 posts won't see the "Thank you" button.)
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mattlach Offline
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Post: #29
(2017-02-13 02:58)nickr Wrote:  There should be no difference in sound quality, although if the audio coming from your TV broadcaster is EAC3 (ie extended not plain ac3) then another thread tells me there might be problems.

Cool, thank you. I have not encountered EAC3 yet, but the encoding standards and sound seem to be on a channel by channel, and even a show by show basis, sometimes each commercial during the commercial break has its own video formatting, audio encoding and shifts between interlaced and non-interlaced. I wish they could just settle on one broadcast standard. at least per channel.

What about the alphabet soup of film standards? You know, Dolby this that or the other, with or without Atmos, and DTS, with or without Master HD or X?

(2017-02-13 02:58)nickr Wrote:  Set speakers on 5.1 (in kodi) if you have 5.1 real speakers.

Ahh, thanks. Right now I have it in 7.1 mode, and output configuration to "best match".

This appears to not upmix, but rather decode the channels it has, and send them along to the receiver.

For most TV content, the receiver seems to receive 5.1 channels as expected. I haven't tested a film encoded with 7.1 yet, but my expectation is that then it would send along the 7.1 channels, and my receiver would identify it as such, and engage the "Neural X" mode which uses its DSP to make the most out of those 7.1 channels and mix them together to output them over my 5.1 speakers.

After all, this is how it would work in audio pass-through mode. The receiver would receive all the audio channels that the content has, and mix them to the best of its ability.

No offense to the Kodi team or the underlying code it uses to mix audio (ffmpeg?) but unless I have evidence to the contrary, I feel like I trust my Denon receiver and it's DTS Neural X downmix/spacial remapping algorithm more with this task.

I could be wrong though, so if I am, please educate me! Tongue
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nickr Offline
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Post: #30
You're over my pay grade now.

If I have helped you or increased your knowledge, click the 'thank user' button to give thanks :) (People with less than 20 posts won't see the "Thank you" button.)
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